1. Field of the Invention
The present invention relates to integrated circuit technology and to charge pump circuits for use in integrated circuits. More particularly, the present invention relates to charge pump circuits for providing intermediate voltage potentials in integrated circuits.
2. The Prior Art
Charge pump circuits are known for providing both positive and negative voltage potentials in integrated circuits. It is, however, difficult to generate charge pump voltages that are slightly above the supply voltage because of the nature of charge pump circuits. FIG. 1 shows a typical prior-art Dickson charge pump circuit in which three diodes 10, 12, and 14 are connected in series between an input node 16 and an output node 18. A clock signal drives a first node 20 common to the cathode of diode 10 and the anode of diode 12 through a capacitor 22. The clock signal is inverted through inverter 24 and the inverted clock signal drives a second node 26 common to the cathode of diode 12 and the anode of diode 14 through a capacitor 28.
As will be appreciated by persons of ordinary skill in the art, each clock pulse will drive the output node 18 up by an amount of voltage roughly equal to VDD−Vt, where VDD is the supply voltage and Vt is the threshold voltage of the diodes. If VDD is 3V, Vt is 1V, every clock cycle will drive the output node 18 up by 3V−1V=2V. If it is desired to regulate the output voltage to 4.5V, there will be a temporary overshoot to 5V, resulting in a very noisy output voltage. This can be avoided by providing fast regulation at the expense of drawing a lot of power or by providing a large capacitor on the output of the regulator. Both of these solutions are less than desirable.